The present invention relates to a filter assembly and, more particularly, to a unique filter structure particularly useful in the filtering of parenteral fluids during the administration of such fluids. The invention further relates to methods for manufacturing the unique filter structure and the filter pouch embodiments usable therewith.
For some time it has been the preferred practice to filter intravenous and other parenteral solutions prior to the administration of such solutions to a patient to remove particulate matter that may be present in the solutions. Many different filter structures have been utilized for this purpose and many different procedures have been devised to insure that the fluids are properly filtered and administered with the highest degree of safety for the patient.
Recently, filter media have become commercially available that permit the filtration of intravenous fluids down to a particle size of 0.22 microns. This is significant in that a filter having this pore size effectively filters out all bacteria from the fluids in addition to removing particulate matter. Heretofore, one of the main drawbacks of utilizing a 0.22 micron filter was that a very high pressure drop was created by the presence of the filter, thus, necessitating the use of a pump to sufficiently overcome the back pressure. Also, the 0.22 micron membrane filter media that have been found to be particularly applicable for use in the filtering of intravenous fluids are exceptionally difficult to handle during the fabrication of the filter media into appropriate filter structures. This is true because most of such filter media have very low tear strengths and do not form adequate heat seals with other plastic materials. Therefore, the geometrical configurations heretofore available with the 0.22 micron membrane filter media have been relatively flat surfaces which greatly limit, because of size considerations, the available filter area for the passage of fluids. Thus, the problem of excessive back pressure is increased because of the relatively small filtering surfaces.
Another problem encountered in the use of prior filters was that of air blockage due to improper priming. Since the type of filters contemplated by this invention are hydrophilic, they do not pass air and, consequently, air accumulates at the filter surface and reduces the available filtration area. The result of this air accumulation at the filter surface is that it reduces the flow rate and contributes to the malfunction of the system. A significant portion of this problem may be overcome by priming the filter assembly prior to its use; however, since all prior filters have been constructed from relatively rigid housing materials, this priming technique has been relatively complicated and has not always been effective in removing all of the air from the filter housing.
It will be apparent from the foregoing discussion that many significant problems have existed in prior attempts to manufacture and use a filter assembly to provide absolute filtration of intravenous and other fluids. These problems are in part occasioned by the difficulty in handling the presently available membrane filter media and by the relatively rigid housing structures that have been heretofore utilized.